ChestLive data

CT Pulmonary Angiography

CT pulmonary angiography is the first-line imaging test for suspected acute pulmonary embolism, directly demonstrating intraluminal thrombus within the pulmonary arteries down to the segmental and often subsegmental level. Optimal timing places peak contrast enhancement in the pulmonary arterial tree, and the study simultaneously assesses right heart strain and provides an alternative diagnosis when PE is absent. Clinical pretest probability and D-dimer should guide appropriate use.

Indications

Suspected acute pulmonary embolism with intermediate/high pretest probability or positive D-dimer
Assessment of clot burden and right heart strain in confirmed PE to risk-stratify
Evaluation of chronic thromboembolic pulmonary disease/hypertension
Hemoptysis workup to assess pulmonary and bronchial vasculature and parenchymal cause
Suspected pulmonary artery anomaly, tumor, or arteriovenous malformation
Pulmonary vascular assessment prior to or after intervention

Contraindications & Cautions

Iodinated contrast allergy: premedicate or consider V/Q scanning as an alternative
Renal impairment: assess eGFR and weigh contrast-associated nephropathy risk; hydrate and consider V/Q
Pregnancy: consider V/Q or perfusion scintigraphy to reduce maternal breast dose; if CTPA performed, use dose-optimized protocol
Inability to hold breath or maintain the required contrast bolus can degrade diagnostic quality
Hemodynamic instability requiring resuscitation before or during scanning; monitor closely

Patient Preparation

Obtain large-bore IV access (18-20 G, antecubital) suitable for high-rate power injection
Screen renal function, contrast allergy, and pregnancy; document Wells/Geneva score and D-dimer
Fasting is not strictly required; ensure resuscitation readiness for contrast reactions
Coach a brief breath-hold at end-inspiration (or shallow suspended respiration to limit transient interruption of contrast)
Position supine with arms elevated; attach ECG if cardiac gating is used
Rehearse breathing instructions to avoid respiratory motion and contrast dilution

Technique & Parameters

Thin-section helical acquisition, 1-1.5 mm collimation, from above the aortic arch (or lung apices) to below the diaphragm
IV contrast 50-80 mL of high-concentration iodinated agent at 4-5 mL/s, followed by a saline chaser
Bolus tracking with ROI in the main pulmonary artery (trigger ~100-150 HU) or empiric ~15-20 s delay
120 kVp standard; lower kVp (80-100) enhances iodine attenuation and reduces dose/contrast in appropriate patients
Caudocranial scanning can reduce respiratory and superior vena cava streak artifact
Reconstruct axial and multiplanar (including oblique) images; measure RV:LV diameter on axial images

Systematic Review

Confirm adequate pulmonary arterial opacification before excluding PE
Trace the main, lobar, segmental, and subsegmental arteries systematically for filling defects
Assess RV:LV short-axis diameter ratio and interventricular septal bowing for right heart strain
Look for reflux of contrast into the IVC/hepatic veins as a strain sign
Evaluate lung parenchyma for infarcts, wedge opacities, mosaic perfusion, and alternative diagnoses
Review the pleura, mediastinum, and any incidental pulmonary nodules
Check the aorta and cardiac structures within coverage for alternative causes of symptoms

Key Findings & Significance

Intraluminal filling defect (partial or complete) forming acute angles with the vessel wall: acute PE
Eccentric, mural, calcified, or webbed defects with vessel narrowing: chronic thromboembolic disease
RV:LV ratio >1.0, septal bowing, and IVC contrast reflux: right heart strain / higher-risk PE
Peripheral wedge-shaped opacity (Hampton hump) or linear band: pulmonary infarct
Mosaic attenuation with pruned vessels and enlarged pulmonary artery: pulmonary hypertension
Bronchial artery hypertrophy and parenchymal cause on hemoptysis studies
Alternative diagnoses: pneumonia, edema, pneumothorax, aortic pathology, or malignancy

Differential Considerations

Central filling defect: acute PE vs flow-related mixing artifact vs pulmonary artery sarcoma
Perfusion mosaicism: chronic PE vs small-airways disease vs pulmonary vascular disease
Right heart strain: acute PE vs pre-existing pulmonary hypertension vs chronic cor pulmonale
Peripheral opacity: infarct vs pneumonia vs hemorrhage vs atelectasis
Enlarged pulmonary artery: pulmonary hypertension (any cause) vs idiopathic dilatation
Apparent subsegmental defect: true clot vs partial volume/motion artifact vs poor opacification

Pearls & Pitfalls

A suboptimally opacified study is nondiagnostic for PE, not negative; consider repeat or alternative imaging
Transient interruption of contrast from deep inspiration dilutes pulmonary arterial enhancement and mimics defects
Beam-hardening and flow artifacts commonly simulate defects; correlate on multiple planes and windows
Report right heart strain because it changes risk stratification and management
Isolated subsegmental PE has uncertain clinical significance; correlate with clinical risk and DVT status
Do not miss an alternative diagnosis (e.g., dissection, pneumonia) that explains the presentation

Structured Report

State protocol, contrast timing, and adequacy of pulmonary arterial opacification
Report presence, location (most proximal level), and extent of emboli, or explicitly state their absence
Include RV:LV ratio and other signs of right heart strain
Describe pulmonary infarcts, parenchymal, pleural, and mediastinal findings
State any alternative or incidental diagnosis explaining the clinical presentation
Impression: PE present/absent with clot burden and strain, plus recommendations for management or follow-up

References

ACR Appropriateness Criteria: Suspected Pulmonary Embolism
ESC Guidelines for the Diagnosis and Management of Acute Pulmonary Embolism
PIOPED II Investigators (Stein et al.), NEJM: Multidetector CT for Acute PE
Fleischner Society statement on subsegmental pulmonary embolism

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.

CT Pulmonary Angiography

📋 Indications

⛔ Contraindications & Cautions

🧑‍⚕️ Patient Preparation

⚙️ Technique & Parameters

🔎 Systematic Review

🩻 Key Findings & Significance

🧠 Differential Considerations

💡 Pearls & Pitfalls

📝 Structured Report

📚 References